THE SPERMATOGENESIS OF UMBRA LIMI. 139 



8. During diakenesis tetrads of the closed ring type appear. 

 Final tetrad-formation is accomplished by the contraction of 

 such rings. Carefully stained preparations show clearly the 

 quadripartite nature of the tetrads in advanced metaphase when 

 viewed from one pole. 



9. Transversely constricted chromosomes are found in Umbra, 

 but they are limited to certain spermatogonial divisions and play 

 no part in the maturation divisions. 



10. The tetrads have a median fiber attachment and separate 

 into dyads at the metaphase of the first maturation division by 

 a pulling apart at the apices of the loops or Vs. 



11. The secondary spermatocytes may go into a resting stage 

 ibut usually the telophase of the primary spermatocyte passes 



mmediately into the metaphase of the second maturation 

 division. The separation of the dyads at the second maturation 

 division is very rapid. 



12. No unusually large or lagging chromosomes were observed 

 in the first or second maturation divisions. 



13. The nuclear material of the transforming spermatid goes 

 through an apparent fusion of chromatin masses, with a subse- 

 quent peripheral condensation of the chromatin, and a contraction 

 of the entire nucleus as the head of the spermatozoon forms. 



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